In recent years, image forming apparatus wherein electrophotography is adapted, such as electrophotographic copying machines, electrophotographic laser printers and the like have become common in our society. In one well known form of electrophotographic copying machine, as shown in FIG. 9, a photoreceptor 24 disposed rotatably in the direction of the arrow A is first uniformly charged by a charger 25 and exposed to a reflected light 26 from the surface of an original, thereby forming an electrostatic latent image. The electrostatic latent image is formed into a visible image by applying toner stored in a developing device 27. This visible toner image is transferred onto a copy sheet 28 by a transferring device 29, to be fixed by a fixing device (not shown), and then the copying sheet 28 having the toner image thereon is discharged from the body of a copying machine. There remains on the surface of the photoreceptor 24, about twenty percent of toner used for toner image formation. The residual toner is scraped off and removed by a blade 30a of a cleaning device 30. Thereafter, the electric charge on the photoreceptor 24 is eliminated by a static eliminator 31 and the next cycle of copying operation is commenced. Generally, this static eliminator 31 comprises a static eliminating lamp or the like for eliminating the electric charge with light projected therefrom, or alternatively has the same structure as that of the charger 25. Such a static eliminator device 31 is essential to an electrophotographic copying machine, since if the copying machine is designed without the static eliminator 31, the surface potential at the photoreceptor 24 will continuously increase due to continuous charging by means of the charger 25. This causes troubles such as a dielectric breakdown in the photoreceptor or the like because of overcharging.
While the personalization of electrophotographic copying machines is expedited recently, a need for small-sized and low-priced copying machines is increasing. Conventional copying machines having such a static eliminator 31 can, however, no longer meet the above need.
A charger having a gird provided therein, i.e., a scorotron charger has been generally used for the purpose of overcoming the above problems. In the use of the scorotron charger, when the potential is lower at the photoreceptor 24 than at the gird, a charge applied the photoreceptor 24 by the scorotron charger is preferentially applied to the photoreceptor 24, while the charge preferentially flows to the grid in the case the potential of the photoreceptor 24 becomes close to the potential of the grid. Hence, the potential of the photoreceptor 24 can be maintained at a specified level without using the static eliminator 31. Specifically, in the use of the scorotron charger, the grid prevents overcharge caused by continuously charging the surface of the photoreceptor 24, and allows the photoreceptor 24 to be uniformly charged without using the static eliminator. This contributes to the miniaturization of copying machines.
Although the overcharge can be prevented by the above scorotron charger, there still remains such a drawback that the quality of reproduced images is deteriorated due to a change in the surface potential of the photoreceptor 24 occuring after the initial rotation period (several rotations) of the photoreceptor 24.
Furthermore, high processing and assembling accuracies are required for the cleaning device and charger, and therefore there is a difficulty in miniaturizing copying machines.
A charger 25 having a charging wire 25b for releasing a corona charge and stretched within a metal frame 25a, has been generally used as the charger 25. This type of charger is conventionally formed as a single unit, and the frame 25a is formed for the charger's exclusive use. Hence, there has been a strong need for parts which can be used for multiple purposes in order to produce small-sized and low-priced copying machines.